Electroacoustic transducers for submarine echo sounding



y 1967 E. AHRENS ETAL ELECTROACOUSTIC TRANSDUCERS FOR SUBMARINE ECHOSOUNDING 4 Sheets-Sheet 1 Filed June 11, 1965 FlG.l

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y 16, 1967. E, AHRENS QETAL 3,320,578

UBMARTNE ECHO SOUNDING Filed June 11, 1 965 4 Sheets-Sheet 2 Fl G. 3 24,

y 16, 1967 E. AHRENS ETAL ELFICTROACOUSTIC TRANSDUCERS FOR SUBMARTNBECHO SOUNDING Filed June 11, 1965 4 Sheets-Sheet 3 FIG. I?

FIG44 Hul O May 16, 1967 E. AHRENS ETAL 3,320,578

Y ELECT OOOOOOO IC TRANSDUCERS FOR SUBM AAAA NR ECHO S0 TTTTTT 1 G FiledJune 11, 1965 FIG-5 FIG..6

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4 Sheets-Sheet for determining the depth of the net.

3,320,578 ELECTROACOUSTIC TRANSDUCERS FOR SUBMARINE ECHO SOUNDING ErhardAhrens and Karl Fcher,-bth of Kiel, Germany,

assignors to Electroacustic G-esellschaft mit beschrankter Haftung,Kiel, Germany, a corporation of Germany Filed June 11, 1965, Ser. No.463,257 Claims priority, application Germany, June 15, 1964,

E 27,220 28 Claims. (Cl. 340-8) Our invention relates to electroacoustictransducers for submarine echo sounding (sonar).

When working with echo sounding devices to determine the presence ofcertain objects in bodies of water, the particular objects may besituated at relatively large depths. This happens, for example, insearching for sunken wrecks, when tracking schools of fish with adragnet, or when applying sonar techniques for exploratory purposes suchas offshore drilling for oil. When soundings are taken from the surfaceof the body of water, the resolution of the recorded reflections is veryslight. Thus, even with a transducer characteristic having an openingangle as small as approximately 10, which can only be achieved withgreat effort, there results a reflection from an area of 100 metersdiameter at a depth of 600 meters.

It is possible, for example, to improve the resolution by usingnet-supported sonar probes, inasmuch as the net itself can be draggedbehind a ship at a depth of 500-600 meters, this net carrying anoscillator for tracking a swarm of fish in the vicinity of the netopening or It is possible also to increase the resolution by takingsoundings from an unmanned container dragged by a suitable drag line,the components of the sounding equipment, such as the recorder,transmitter, receiver, and at least a transducer, being mounted in'thiscontainer. This permits sounding from a considerably shorter distance,for example only 100 meters from the sea bottom which may have a depthof 600 meters. With a beam opening angle of 10 an area of 17 m. diametercan thus be resolved. By changing the depth of the transducer-carryingcontainer, the sonically impinged area and consequently the resolutionof details in the recording can be varied within wide limits. Forexample, by first producing survey pictures with the aid of recordingsat which the transducer or container is located at a larger height abovethe sea bottom, any particular localities of interest can then berecorded with greater resolution by lowering the transducer'andperforming the sounding from a smaller distance above sea bottom.

When carrying out operations of the above type, the problem of highpressure is encountered. At a depth of 500 meters, for example, thepressure may be in the order of 50 atmospheres. As a result,considerable dif- United States Patent ficulties are encountered in theconstruction of a transducer which is required to operate effectively athigh hydrostatic pressures while at the same time being required, inspite of these high pressures, to fulfill a number of furtherrequirements in such a way that the fulfilling of certain requirementsin no way conflicts with the fulfilling of other requirements.

In addition to encountering problems of this latter type in anindividual electroacoustic transducer, particular problems arise when aplurality of transducers are assembled into a group. Extreme difficultyis encountered in arranging the forwardly directed outer surfaces of thediaphragms of such transducers close enough to each other to providesharply concentrated primary radiations with minimum secondaryradiations. This is particularly true of electroacoustic transducerswhere the oscillatory diaphragms are connected by an elastic means tothe transducer housings for oscillatory movement relative thereto. Wheresuch elastic connections between the diaphragms and housings are notused, it has been possible to provide an arrangement where the radiationreceiving or emitting surfaces of the diaphragms are situated quiteclose to each other, but these structures do not have a high efiiciency,because they unavoidably short-circuit the projecting portions of theexterior forwardly directed diaphragm surfaces, so that theseshort-circuited surface portions cannot effectively transmit or receiveradiations. This undesirable effect increases where the forwardlydirected surface areas of the various diaphragms of such an assembly areof approximately the same area, as the central effective area, inasmuchas the size of the area increases as the square of the radius thereof.Therefore, the outer surface portions adjacent the periphery of thediaphragms are ineffective for radiation purposes while the actuallyeffective central portions of the radiating areas are not situated asclose to each other as appears from the exterior of the structure, sothat in spite of the fact that the several transducers of the group arestructurally situated quite close to each other, the same disadvantagesare encoun- I tered in connection with radiations as with the structureswhere the diaphragms are connected by an elastic means to the housingsfor oscillatory movement relative thereto.

Moreover, with structures of the above type the transmitted frequencyband is undesirably narrow inasmuch as this factor is determined by therelation between the emitting (or receiving) area F to the actualmechanical or physical area F of the active transducer element. As aresult of the short-circuiting of the peripheral portions of theadjoining diaphragms of a group, as referred to above, where there isonly an apparently large emitting or receiving area, a large part ofotherwise effective emitting or receiving area. is excluded, so thatwith structures of this type the effective emitting area is onlyapproximately as great as the physical area of the active transducerelement, and thus F reF To provide for shielding against undesirableradiations, it has been known to arrange outside of the emitting area ofthe diaphragm a porous and/o1" air-containing body. Such bodies,however, neither have any desirable resistance to pressure nor permitthe transducer to be covered by a coating which is resistant to pressureand which protects against corrosion, so that structures of this type donot lend themselves to efiicient operation at relatively great depths inthe bodies of water.

It is accordingly a primary object of our invention to provideindividual and groups of transducers which will avoid or greatlyminimize the above-mentioned drawbacks and will instead permit highlyefficient operation at great depths in bodies of water.

Thus, it is an object of our invention to provide a transducer which,with respect to etliciency, coupling factor, frequency band, radiationconcentration, and impedance, fulfills all of the desired requirementswhile at the same time having a perfect seal of the interior of thetransducer with respect to the exterior thereof and providing greatresistance to constant jarring of the transducers in such a way that itis possible to fulfill all of these requirements and achieve asufiiciently concentrated radiation beam of a plurality of transducerswhich can be arranged in a group without Wasting too much energy onsecondary radiations of the characteristic.

Another, more specific, object of our invention is to provide anelectroacoustic transducer capable of sending or receiving radiations inliquid and suited for operation at great depths while being capable ofbeing arranged in compact groups with the diaphragms of the severaltransducers respectively driven by active elements thereof.

The objects of our invention further include the provision oftransducers capable of being arranged in groups with the outerperipheral edges of the forwardly directed as great hydrodynamicpressures, while also being quite insensitive to explosions, as isrequired when taking seismographic measurements.

In addition, it is an object of our present invention to providetransducers which have a high efficiency as well as large couplingfactors and which can transmit through wide frequency bands as well asbeing capable of being arranged in groups where the individualtransducers can have their forwardly directed emitting (or receiving)surfaces of their diaphragms arranged quite close to each other withoutany interfering intermediate spaces therebetween, so that it is possibleto achieve a highly concentrated beam of primary radiations with a smalldegree of secondary radiations.

Furthermore, the objects of our present invention include thepossibility of applying the principles of the invention to manydifferent types of transducer structures, such as, for example,transducers where the diaphragm is carried by the active driving elementof the transducer as well as transducers where the diaphragm isconnected to the transducer housing by way of one or more elasticconnections. In the latter type of structure the transducers of thepresent invention will have the elastic connecting means arranged nextto a shielding chamber which shields out interfering radiations.

In particular, the objects of our invention include the provision ofelectroacoustic transducers where substantially the entire, forwardlydirected, outer physical surface area of the diaphragm can effectivelytransmit or receive radiations, so that F F and thus a large band widthand a high efficiency can be achieved.

The objects of our invention also include a transducer structure where,even though a plurality of transducers are situated quite close to eachother, nevertheless the walls of the transducer housings can be madequite thick so that they will have a large mass, thus increasing the ef:ficiency inasmuch as transducer housings of large mass will remainrelatively stationary.

In addition, the objects of our invention include the provision oftransducers which can be enveloped in a pressure-resistant andcorrosion-resistant coating without in any way detracting from theefficiency of the operation of the transducer or group of transducers.

In addition, the objects of our invention include the provision oftransducers having structures which enable them either to be constructedas complete individual transducers each having their own housing, withthe housings arranged next to each other when the transducers arecollected in a group, or a structure where each transducer does not haveits own individual housing and instead a plurality of fully operativetransducers are arranged in a common housing.

Primarily, according to our present invention, the transducer includes aplurality of components arranged along a longitudinal central axis ofthe transducer and cooperating together to provide a completelyoperative transducer. These components include a diaphragm which has aforwardly directed outer surface capable of sending and receivingradiations. In accordance with the present invention, this forwardlydirected diaphragm surface will project onto a plane normal to thelongitudinal central axis an area which is at least substantiallycoextensive with the largest area projected onto this plane by any othercomponent of the transducer. The diaphragm of the transducer of thepresent invention has, to the rear of its forwardly directed surface,additional surface area with which a second component of the transducercooperates to define a shielding chamber capable of shielding outinterfering radiations of the rear peripheral surfaces of the diaphragm,and this shielding chamber is highly resistant to pressure.

The invention is illustrated by way of example in the accompanyingdrawings which form part of the application, and in which:

FIG. 1 is a longitudinal sectional elevation of an embodiment of anelectroacoustic transducer according to the invention, the section ofFIG. 1 being taken in a plane which includes the longitudinal centralaxis of the transducer;

FIG. 2 is a longitudinal sectional elevation fragmentarily illustratinghow a pair of transducers can be arranged to form a group or part of agroup of transducers;

FIG. 3 is a fragmentary sectional elevation illustrating anotherembodiment of a transducer;

FIG. 4 is a fragmentary schematic plan view of transducers of theinvention combined in a group;

FIGS. 5-12 are sectional elevations of different configurations of partof a transducer of the present invention;

, FIG. 13 is a fragmentary sectional elevation of another group oftransducers of the present invention;

FIGS. 14 and 15 are fragmentary sections of two other transducers of thepresent invention;

1 FIG. 16 shows another embodiment of a group of transducers of ourinvention; and

FIG. 17 is'a longitudinal sectional elevation, schematicallyillustrating still another embodiment of a transducer according to ourinvention.

Referring now to FIG. 1, the illustrated transducer according to ourinvention is made up of a plurality of coactive components all of whichare arranged along a longitudinal central axis of the transducer. Thecomponents include an active driving or driven oscillator element 1opertaively connected with a diaphragm composed of parts 2 and 2a whichare connected to each other to form a piston-like oscillatory diaphragm.The transducer further includes a housing part 4 and an elastic means 3connecting the diaphragm 2, 2a to the housing part 4 for oscillatorymovement relative thereto in response to the drive from the activeelement 1. A counterweight '13 is afiixed to that side of the activetransducer element 1 which is directed away from the diaphragm 2, 2a.The counterweight 13 is affixed to an insulating plate 57 which is inturn affixed to the active transducer element 1. Moreover, thecounterweight 13 is connected through the elastic elements 14 with arigid.

part 15 which is affixed to the housing. The elastic means 3 as well asthe elastic elements 14 are capable of resiliently yielding duringoperation of the transducer. At its exterior surface, the part 15 isformed with recesses 25a for receiving a layer of cement by which thepart 15 is affixed to the housing part 4. i

The counterweight 13 together with the junction for the electricalconductors are closed off from the exterior 'by a pressure-resistant andwater-tight cap 18 which also forms a part of the housing, and thishousingpart or cap 18 also serves to guide the cable of the transducerto the exterior thereof. This cap or housing part 18 is connected withthe housing part 4 by way of a resilient compressible seal 16 in theform of an elastic member extending between and cemented to the housingparts 4 and 18. The entire transducer is enveloped and closed off fromthe exterior in a gap-free manner by means of a corrosion-resistantrubber or plastic covering or layer 11 which is incapable of reactingwith water, and it will be noted that the elastic sealing structure 16is formed by a pair of inwardly directed flanges of the plastic coating11, these flanges directly engaging and being bonded to each other aswell as to the surfaces of the housing parts 4 and 18 which are directedtoward each other in the manner illustrated in FIG. 1. These flanges arenot only sealed against each other but also against the annular housingsurfaces of the parts 4 and 18, respectively, which are directed towardeach other, and it is the material of the plastic or rubber coating 11which is elastic and yieldably compressible so as to form the elasticsealing structure 16 shown in FIG. 1. The cable 20, which extendsoutwardly beyond the housing part 18 to the exterior, is

surrounded, in the opening of the housing part 18 through which thecable 20 extends, by a tension-relieving spring ring '21. The conductors22 are electrically connected with the active transducer element 1 byway of the soldering assembly 23 to which the conductors are soldered soas to be supported thereby, and the structure 23 is connected to thecounterweight 13 while the conductors are electrically connected withthe active'element 1.

The active transducer element 1 can take the form of any known drivingor driven transducer element operating according to any well establishedprinciple, such as, for example, electrostrictive, magnetostrictive, orpiezoelectric principles. The element 1 can take any of a number ofdifferent geometric configurations such as, for example, cubic, tubular,and/ or multi-layer configurations, and with this latter constructionthe different layers would be parallel to each other and to thediaphragm 2, 2a, as well as perpendicular thereto. The transducerelement 1 serves to convert electrical energy into acoustic energy or toconvert acoustic energy into electrical energy. The acoustic energy isemitted from the radiation surface 8 of the membrane 2, 2a, this surface8 being an outer forwardly directed surface of the diaphragm. The outerforwardly directed surface 8 of the diaphragm 2, 2a is adapted to sendor receive the radiations. The diaphragm is coupled to the activetransducer element 1 by way of the insulating plate 57'. By suitablyarranging the transducer, particularly with respect to the polaritythereof, it is ossible to eliminate one or both of the insulating plates57 and 57'. The coupling can, for example, take the form of cementing.The recesses 25 formed in those rear surfaces of the diaphragm elements2 and 2a which are directed downwardly, as viewed in FIG. 1, are adaptedto receive layers of cement for fixing the components to each other. Theelastic means 3, which connects the diaphragm 2, 2a to the housing 4foroscillatory movement relative thereto, has a structure which enables itto' withstand a high hydrostatic pressure, but at the same time in sucha way that'no appreciable energy is transmitted from the diaphragm 2, 2ato the housing 4 through the elastic means 3.

As may be seen from FIG. 1, according to one of the more importantfeatures of the present invention, the outer, forwardly directed surface8 of the diaphragm, which is adapted to send or receive the radiations,when projected onto a plane normal to the longitudinal central axisalong which all of thetransducer elements are arranged, has an areawhich is'at least substantially coextensive with the largest areaprojected onto this plane by any other component. Thus, ,in theillustrated example the largest area will be projected onto this planeby the housing part 4 which, it will be noted has an outer periph eryonly slightly greater than the outer periphery of the surface 8, so thatthis surface 8 does indeed cover an area which, if not as large as thelargest area projected onto a plane normal to the-longitudinal centralaxis by any component, is at least almost as large as the largest area,and it is in this way that some of the outstanding results of thepresent invention are achieved, as will be apparent from the descriptionwhich follows.

According to another important feature of our invention, there isprovided with the transducer of the invention a pressure-resistant,shielding chamber situated to the rear of the outer forwardly directedsurface 8 of the diaphragm.

In the embodiment of FIG. 1, this radiation shielding chamber takes theform of a relatively narrow annular gap 5 which coaxially surrounds thediaphragm 2, 2a. This gap or chamber 5 is defined on the one hand by theadditional surface area 7 of the diaphragm, this latter area being inaddition to the outer forwardly directed surface 8 thereof, and theinner surface 6 of the housing part 4. In this way the rearwardlysituated surface area 7 of the diaphragm, located at the peripheral edgethereof, is shielded by an air cushion which prevents formation of anacoustic short circuit as well as preventing any interfering radiations.In contrast to known constructions, of the type referred to above, theradiation-shielding chamber 5 is capable of satisfactorily fulfillingits intended function even at high hydrostatic pressures.

A further highly advantageous feature resides in extending the annulargap 5 on the one hand inwardly all the way up to the elastic means 3 andon the other hand outwardly all the way up to the emitting or receiving,forwardly directed, outer surface 8 of the diaphragm. With thisconstruction it is possible to have the advantage of situating theentire transducer within a corrosionresistant plastic or rubber coating11 which envelops the transducer on all sides thereof so that thetransducer is completely closed off from the exterior by the protectivecoating 11, and in spite of this construction the movement v of thediaphragm itself is not obstructed in any way.

A further feature of the construction shown in FIG. 1 resides incovering-the outer end 10 of the gap 5, situated at the outer peripheraledge of the forwardly directed diaphragm surface 8, by means of anelastic material 9. It is to be noted that the gap 5 has a thicknesswhich gradually increases from its end 10 toward the elastic connectingmeans 3, so that the thickness of the gap 5 is at a minimum at its outeropen end 10, and in this way it is possible to provide apressure-resistant elastic closure of the gap without obstructingmovement of the diaphragm 2, 2a even when the transducer is providedwith the protective coating 11. Thus, it is notessential to maintain thegap 5 throughout as small as its size at the elastically covered end10,'and instead it is of advantage to provide the gap 5 with different,or even alternating, thicknesses between its ends. It has been found tobe of advantage to provide an elastic covering 9 which is of an angularcross section so as to extend over and engage the corner at the end ofthe transducer where the forwardly directed emitting or receivingsurface 8 of the diaphragm is situated. way there is providedan'extrcmely compact and at the same time stable closure for the outerend of the annular gap 5.

In the embodiment illustrated in FIG. 1, the annular gap 5 is formed byextending the side wall of the housing part 4 all the way up to theforwardly directed surface 8 of the diaphragm 2, 2a, beyond the elasticmeans 3, and the outer diaphragm element 2 is seated upon-and fixed tothe diaphragm carried 2a so that it is between the housing -part 4 whichextendsforwardly beyond the elastic means 3 and the forward part 2 ofthe diaphragm that the annular gap 5 is for the most part formed. It isthus possible with this construction to construct the carrier element 2aof the diaphragm in such a way that it therewith, thereis provided a gap5 which is defined by 7 very smoothly and cleanly machined surfaces 6and 7, and as a result the width of the gap can be maintained at a verysmall size. Furthermore, it is possible in this way to make a diaphragmquite rigid and at the same time In this rearwardly toward the interiorof the housing.

very light. The diaphragm can be made, at its part 2, of a materialwhich is lighter than the material used for the housing. A further wayof saving weight, while retaining rigidity, is to provide a structure,as shown, where the side surface of the diaphragm part 2 forms part of acone which extends inwardly toward the longitudinal central axis of thetransducer. Also, it is in this way easier, in the interest of achievinga high efficiency, to make the entire housing 4 as heavy as possible, incomparison with the diaphragm part 2.

FIG. 2 illustrates, in section, how individual transducers constructedas shown in FIG. 1, and of course each completely operable as a separateunit, can be combined together to form a group of transducers. It is tobe noted that the outer peripheral edges a of the diaphragms 2, 2a,shown in FIG. 2, extend outwardly beyond the elastic connecting means 3,the housing interiors 4a, and the greatest part of the thickness of theouter walls of the housings 4, 18 so that these peripheral edges ofadjoining transducer diaphragms are quite close to each other, and itis, of course, in this way that the radiation-shielding chambers 5 areformed between the membrane part 2 and the housing part 4, respectively.

Further features of our invention reside in defining part of theradiation-shielding chamber 5 by theelastic means 3 itself, so that inthis way the complete freedom of movement of the elastic means isretained, and also,

in accordance with our invention, the radiation-shielding chamber 5 isseparated from the interior 4a of the housing by means of the elasticconnecting means 3. As is also shown in the embodiments hereinafterdescribed, there are many different possibilities according to whichtransducers may be constructed in accordance with the invention, withthe radiation-shielding chambers taking widely different forms andarrangements, as is also true of the elastic connecting means of theinvention.

Preferably, the elastic connecting means 3 is arranged in such a waythat it is situated in the immediate vicinity of, or directly at, theinner diaphragm surface 12 of the diaphragm part let, this inner surface12 being directed In this way, the requirements with respect topressure-resistance as well as those of providing sufficientyieldability of the elastic means are both capable of being fulfilled.The pressure-resistance is enhanced by providing a structure where thepressure forces acting between the diaphragm and the housing areabsorbed not only by the elastic means 3 but also (FIG. 1) by theelastic connecting structure,14, between the counterweight 13 and thepart which is fixed to the housing, as described above. The transmissionof forces takes place from the diaphragm through the active transducerelement 1, the counterweight 13 and the elastic connecting structure 14to the part 15, which is afiixed to the housing. The part 15 is atfixedto the housing part 4, by being cemented thereto, for example. In thisway the counterweight 13 can be made of a heavier material than thatused for the housing part 4 or the diaphragm, so that the transducer isnot only pressure resistant but also is capable of operating in a wideband. A maximum reduction in the load on the elastic connecting means 3is achievedv if, instead of an elastic connection 14, a rigid connectionbetween the counterweight and the housing is provided. With such aconstruction, it will indeed be possible to provide a larger band width,but also a lower efficiency would re sult, so that according to theparticular purposes for which the transducer of the invention isdesigned, the choice will be made between an elastic connection 14 forinterconnecting the counterweight 13 with the housing part 15, or arigid connection between the parts 13 and 15.

A further possibility for rendering the transducer resistant to highpressure while at the same time providing an elastic connection 3, or 3and 14, which is as soft as possible, so that in this way the smallestpossible loss of energy to the housing 4 is achieved, resides indesigning the pressure resistance of the elastic connecting means 3, or3 and 14, with a narrow tolerance at the range where the maximumoperating depth is to be expected, and providing a protecting meanswhich, when the maximum permissible stressing of the elastic means isexceeded, will protect against damaging the transducer because of thenarrow tolerance of the stressing range of the elastic connecting means.For example, this protective means can be provided by choosing the widthof the radiation-shielding gap 5 in such a way that at its narrowestpart it is only so wide that when the diaphragm is loaded to such anextent that the opposed side surfaces of the shielding gap engage eachother, the elastic connecting means 3, or 3 and 14, between thediaphragm and the housing has not yet reached its yield point. However,the annular shielding gap or chamber must be selected at a size greatenough so that during normal operations free oscillatory motion of thediaphragm is not prevented.

The construction according to this feature can, for eX- ample, becarried out in such a way that behind the diaphragm part 2, the housingis provided with an annular stop shoulder 55 which is directed toward acooperating annular stop shoulder 56 of the diaphragm part 2. Theshoulder 55 of the housing is situated in the path of inward movement ofthe shoulder 56 of the diaphragm part 2, and the distance between theannular shoulders 55 and 56 is selected so as to be great enough duringnormal operation to provide for unrestricted free oscillatory movementof the diaphragm. On the other hand, the distance between the stopshoulders 55 and 56 is selected to be small enough so that when anexcessive pressure on the diaphragm, which would otherwise result inoverloading the elastic connecting means 3 and 14, is encountered, thestop shoulder 56 engages the stop shoulder 55 to prevent damaging of theelastic connecting means.

The safety of the transducer, against being damaged at the highestpermissible pressures, is further enhanced by providing for thecompressible sealing means 16 also a limiting stop shoulder arrangementwhich will limit the extent to which the sealing means 16 can becompressed by the displacement of the housing parts 4 and 18 toward eachother. For this purpose the housing part 4 is'provided with a stopshoulder 17 directed toward an annular surface 17a of the housing part18, so that these surfaces 17 and 17a directly engage each other afterthe sealing structure 16 has been compressed to a predetermined extent.

As pointed out above, the elastic sealing structure is situated betweenthe housing parts 4 and 18 and is formed from the protective coating 11.In addition, it is possible to further protect the elastic seal 16 byway of an outer relatively wide elastic band 19 which surrounds andengages the coating 11 and extends across the latter at its portionswhich extend inwardly to form the seal 16. The surfaces 17 and 17adefine between themselves the narrow gap 52, and the gap 53 between thehousing part 15 and the housing part 18 isof the same thickness as thegap 52, so that at average pressures the sealing structure 16 will becompressed, placing the surfaces 17 and 17a in engagement with eachother and thus placing the inner housing part 15 directly in engagementwith the housing part or cover 18, so that the cement connection betweenthe inner housing part 15 and the housing part 14, as well as theelastic sealing structure 16, is not stressed by the hydrostaticpressure acting between'the diaphragm' and the housing this is broughtabout by an additional annular body 24, which serves to complete thehousing and extend into the annular groove which would be presentwithout the body 24. It is the inner surface of this body 24, whichforms a part of the housing, which defines the outer limit of theannular gap 5. With this construction there is, on the one hand,sufficient space for machining the surfaces which determine the size ofthe gap 5, and, on the other hand, it is possible to maintain for thisgap an extremely small size. The body 24 can, for example, be made up ofa number of elements which are of arcuate configuration and which arearranged together so as to form a complete ring. Thus, with thisconstruction it is possible to insert the individual elements of thering 24 radially into the position indicated in FIG. 3. For the purposeof making the diaphragm 2 quite rigid while at the same time as light aspossible, it is preferably composed of a light metal and tapers towardsits center, as indicated in FIG. 3.

In FIG. 1 the diaphragm 2, 2a was composed of a pair of elements afiixedto each other and serving to complete the formation of the gap 5, whilein FIG. 3 it is the body 24 which serves as the element for completingthe housing part 4 and forming the gap 5. The invention, however, canalso be realized in the form of a combination of these features (FIG.15) inasmuch as the known diaphragm 2b shown in FIG. 15 as well as theknown housing 4b illustrated therein, are both completed by additionalele ments 49 and 50, respectively, which are afiixed respectively to thediaphragm element 2b and housing element 4b, and which have theconfiguration shown in FIG. 15 so as to form the gap 5. In this way,with the process of manufacture indicated in FIG. 15, it is possible tomake a transducer according to our invention from a known, conventionaltransducer construction. Thus, with this particular embodiment thestructure shown below the dotted line 48 in FIG. 15 is readily availablein the form of a complete transducer which is conventional, and thisconventional transducer structure can be modified to have the structureof the present invention by completing the transducer structure in themanner shown in FIG. 15 and described above, so that in this waymanufacturing procedures which are conventional and which have beenwidely used up to the present time can be maintained for the most partwithout any change.

Of particular advantage is the feature of the transducer of theinvention according to which the peripheral edge of the diaphragm, atits outer, forwardly directed surface is at least approximatelycoextensive with the outer periphcry of the housing at its top end. Inthis way the emitting or receiving surface 8 is of the same size as, orapproximately of the same size, as the largest cross-sectional area ofthe transducer housing situated behind the forwardly directed diaphragmsurface, or of the element such as the element 24 which completes thehousing so as to form the gap 5. This construction is of particularsignificance when a plurality of transducers are arranged in a groupsince with this construction it is possible to provide a group oftransducers where the individual transducers of the group are arrangednext to each other without any interfering intermediate chamberstherebetween.

Where a plurality of oscillators are arranged in a group, the problem ofmounting and holidng the plurality of oscillators is of considerablesignificance. The

mounting must be constructed in such a way that the emitting orreceiving surfaces of the group-of oscillators have no dead spacesresulting from the structure of the mounting which supports theplurality of transducers. For this purpose, there is provided in oneexample of the structure of our invention, in the exterior surface ofthe side wall portions of the transducer housings, depressions 26,indicated in FIG. 1. These depressions of several housings are situatedin a common plane with adjoining depressions of adjoining housingscommunicating with each other so as to form passages for receiving theconnecting means for interconnecting the several housings to each other.Thus, there is shown in FIG. 4 an example of a suitable structure forinterconnecting a plurality of transducers. The transducers 27 shown inFIG. 4 are of square cross section, so that they can be placed next toeach other without any gaps therebetween. The dotted lines 28 indicatethe outer peripheral edges of the forwardly directed, outer emitting (orreceiving) surfaces of the diaphragms, and it is apparent that in eachtransducer the area of its forwardly directed outer surface 8 fillsalmost the entire cross section of the transducer. The transducers 27are individually inserted into a mounting plate 29 which has theconfiguration of a double H. Thus, as may be seen from FIG. 4, themounting plate 29 has the configuration of a double H where the two Hshave a common leg joining the pair of Hs to each other. As a result, theindividual transducers can he slipped along the legs of the mountingplate 29 with these legs slidably received in the grooves 26, and ofcourse the outer legs 30 of the mounting plate will be situated at theexterior of the assembly. After the plurality of transducers have beenassembled together on the legs of the plate 29, a pair of transverse endbars 31 are fixed to the free ends of the legs of the plate 29, as bybeing bolted thereto, so that in this way, it is possible to mount theplurality of transducers quite close to each other in a group occupyingthe smallest possible amount of space. Of course, the structure of theinvention is not limited to transducers having square diaphragms,inasmuch as transducers having rectangular or hexagonal, as well ascircular, diaphragms can also be used.

The individual transducers can also be grouped to gether compactly inanother way. For example, a mounting plate is formed with openingsspaced from each other by distances suitable for the individualtransducers, and the transducers are interested into these openings fromthe front of the mounting plate, and are affixed to the mounting plateat their rear portions, for example at the rear,housing oncover parts18. The transducer may be affixed, for example, by adhesive or bolts.One possibility resides also in making the mounting plate 29a (FIG. 16)so thick that the openings or bores 40 formed for the individualtransducers have a sufficient depth to constitute in and of themselvesthe interior portions of the transducers, so that these bores 40 canreceive in their interiors the components of the several transducers inorder to replace the individual housings of the plurality oftransducers. Therefore, in the embodiment of FIG. 16, there is but asingle wall 29a formed with the plurality of openings 40 whichrespectively receive the plurality of transducers, none of which includetheir own housings, inasmuch as all of the transducers have in thisembodiment a common housing 29a. With this construction theradiation-shielding chambers of adjoin: ing transducers communicate witheach other so that each radiation-shielding chamber 5a is defined by therearwardly directed surfaces 7a and 7b at the peripheries of thediaphragms of at least a pair of adjoining transducers. A coating 11a,which is common to all of the diaphragms, seals, together with theelastic covering elements 9a, the radiation-shielding chambers 54.

Further embodiments of our invention are illustrated by way of examplein the figures hereinafter referred to. In these embodiments, thediaphragms are indicated by the reference character 2, the elasticconnection means by the reference character 3, and the transducerhousing parts by the reference character 4. The elastic covering for theannular gap is indicated by the reference characters 9 or 9a, while theplastic or rubber covering for the entire assembly is not illustrated.The structures for defining the outer limits of the radiation shieldingchamber, as well as for forming the elastic connection between thediaphragm and the housing and for forming the 1 1 shielding chamberitself, can take the widest variety of forms.

In FIGS. 5 and 11, an annular body 32 of rectangular cross sectionextends forwardly from and forms part of the side wall of the housingpart 4,50 as to determine the outer limits of the shielding chamber 5.This ring 32 can be made of a strong high quality material and thus canbe manufactured-with a relatively small thickness. Furthermore, thisstructure has the advantage of being capable of being mounted around thediaphragm 2 as a single one-piece body, so that dividing of the ring 32up into a plurality of elements is not required. In FIG. 11, the ring orbody 32 can in many cases be dispensed with if the elastic connection 40is situated at the outer periphery of thediaphragm 2. However, the ring32 of FIG. 11 will serve to completely eliminate residual radiationswhich will eventually be present. In the embodiment of FIG. 6,therannular body 33, which completes the housing part 4, has a taperedcross section so that it is of a small thickness at its outer free edgesituated substantially at the same plane as the forwardly directed outersurface of the diaphragm 2. Also, stepped cross sectional areas for thering may be provided, as is shown by the ring 34 in FIG. 7. Such astepped construction is also shown for the ring 35 in FIG. 8, the ring36in FIG. 9, and also the ring 37 inFIG. 10. It will be noted, however,that in the case of the ring 37 of FIG. 10, the dimension of the ring ina direction parallel to the forwardly directed outer surface of thediaphragm is greater than its dimension in a direction parallel to thelongitudinal central axis of the transducer. In the case where aplurality of transducers are combined into a group, it is possible tohave a common body perform the functions of the individual rings 32-37shown in FIGS. 5-10, respectively. In addition, it is not essential thatthe pressure-resistant exterior closure of the radiation sealing chamberbe made of an elastic covering material 9 or 9a, as indicated in FIGS.5-7. Instead, an additional elastic connection 38 (FIG. 8) or 39 (FIG.9) can be provided between the diaphragm 2 and the housing 4, that is,between the diaphragm 2 and the rings 35 and 36 of the embodiments ofFIGS. 8 and 9, so as to close off the outer end of the shielding gapwith this further elastic connectingstructure. In this case, it is ofadvantage in the embodiment of FIG. 8 to pre-stress the elasticconnecting means 38 when the annular body 35 is mounted in the positionindicated in FIG. 8, so that during oscillatory movement of thediaphragm the elastic means 38 cannot become separated from the annularbody 35. Of course, it is also possible, if desired, to fasten theelastic means 38 to the body 35 by soldering, welding, cementing, or

the like.

Also, the elastic connecting means which connects the diaphragm to thehousing can take many different forms and arrangements. In theembodiment of FIGS. 1 and 3 as well as FIGS. 5-10 and 13-16, the elasticmeans 3 is situated in a plane normal to .the longitudinal central axisof the transducer and is bendable in a direction transverse to thisplane. However, it is not essential that the elastic means be flat andextend along a straight line, since the elastic means can be curved orcan have an angular cross section, as is indicated by the elastic means3 of FIG. 7. Also, it is apparent that the location of the connectionbetween the elastic means 3 and the diaphragm can be varied widely. Theelastic connection structures 40 and 41 of FIGS. 11 and 12,respectively, are so formed and arranged that they are situatedsubstantially in a cylinder whose axis includes the longitudinal centralaxis of the transducer, and these elastic structures are designed toyield in the directions in which they extend, that is, in a directionparallel to the longitudinal central axis of the transducer. Thus, itwill be seen that in the embodiments of FIGS. 11 and 12 the elasticmeans 40 and 41, respectively, are in effect extensions of the sidewalls of the housing part 4. The elastic means 41 shown in FIG. 12 caneither be situated in the illustrated position .where it forms anextension of the exterior surface of the side wall of part 4, or it canbe arranged closer to the longitudinal central axis of the transducer,where the inner surface of the elastic means 41 forms an extension ofthe inner surface of the side wall of the housing part 4. .In the latterconstruction, the diaphragm 2 of course extends radially outwardlybeyond the elastic means 41. For example, the elastic means 40 of FIG.11,

I or the elastic means 41 of FIG. 12, can be situated at any desiredlocation within the chambers 42 and 43 while maintainingthe illustratedmagnitude of the diaphragm.

One special embodiment of a transducer according to the presentinvention does not include any elastic connecting means 3 between thediaphragm and the hon-sing. In this case, it is the elastic coveringstructure 9 which takes over the role of the elastic means, the elasticcovering 9 operating together with the plastic or rubber envelope 11, inthis case, to perform the function of the elastic connecting meansbetween the diaphragm and the housing, a-s well as to provide apressure-resistant seal of the interior of the transducer from theexterior thereof. A' construction of this type is illustrated in FIG. 17in a longitudinal sectional elevation. Referring to FIG.

17, it will be seen that the radiation-shielding chamber 5 has at theright side of FIG. 17 a cross-sectional configuration somewhat differentfrom its configuration illustrated at the left side of FIG. 17, so thatFIG. 17 illustrates how it is even possible according to the presentinvention to provide a radiation-shielding chamber which need not be ofuniform cross section circumferentially with respect to the longitudinalcentral axis of the transducer, although, of course, the transducer maybe provided with a uniform cross section of the chamber 5, eitherconforming to the cross section shown at the right side of FIG. 17 orwith that shown on the left side of FIG. 17. In this embodiment, it isto be noted that the transducer housing formed by the parts 4, 24a, and18 has a tapered configuration making it possible to arrange thetransducer on a curved surface such as a cylindrical surface. Inotherwords, where the supporting plate which carries a plurality oftransducers is curved so as to extend along a cylinder, for example, ifthe housings of the transducers have the tapered configurationillustrated in FIG. 17, they can be arranged in close proximity to eachother in side-by-side relation with a minimum of spacing therebetween,even though the plate, whose legs are received in the grooves 26 asdescribed above, is not fiat but instead extends along a cylinder orother suitable curve. Thus, even under these conditions, the transducerscan be arranged in very close proximity to each other. Thus the emittingor receiving surfaces of the diaphragm can under these conditions alsohave a minimum of space therebetween. The parts which are illustrated inFIG. 17 and which correspond to those of FIGS. 1 and 3, for example, aredesignated by the same reference characters. Thus, the housing part 4supports the member 24a, which forms part of the housing and whichdefines the outer limit of the annular shielding chamber 5. As indicatedabove, there is no elastic connecting means integral with the housing,for example, and instead the elastic connecting means is formed bytheyieldable sealing structure 9a, which closes the outer end of thechamber 5, this yieldable sealing structure being itself covered by theplastic or rubber envelope 11 which also participates in the elasticmounting of diaphragm 2 with respect to the housing 4, 24a, 18. -It willbe noted that with this construction the envelope 11 has between thehousing parts 4 and -18 inwardly directed flanges forming the elasticmeans 16. Also FIG. 17 shows the cable 20 extending through the tubularcable outlet of the cap or housing part 18 where the tension-relievingspring ring 21 is provided, and FIG. 17 also fragmentarily illustratesthe electrical conductors 22. Furthermore, the active element 1connected to the diaphragm 2 is illustrated, and of course thisimportant element is in turn connected to the'counterweight 13 which isconnected by the elastic means 14 to the housing part 4.

In the particular embodiment shown in FIG. 17 it is possible for thetransducer housing part 4 to have at its lower portion, in the region ofthe mounting groove 26, a circular cross section while, for example, thediaphragm 2 as well as the housing part 24a situated directly behind thediaphragm have a hexagonal cross section. Therefore, with such aconstruction the housing part 24a not only participates in theformationof the radiation-shielding chamber 5, but in addition it serves toprovide a transition between the different cross sectionalconfigurations of the diaphragm 2 and the housing 4.

Furthermore, FIGS. 5-16 demonsetrate that the pressure-resistantradiation-shielding chamber need not be limited to the particularconfiguration illustrated. in FIGS. 1-3. In the first place, the annulargap 5 of FIGS. 1-3, can extend along and form part of acone or a sphere,as well as a cylinder. Also, the annular gap can have one or more sharpangles in its cross sectional configuration as well as different widthsin its cross sectional configuration. Moreover, the radiation-shieldingchamber need not necessarily be separated from the interior ofthehousing, as is demonstrated by FIGS. -12, where the sound orradiation shielding chamber includes the portion 42 (FIGS. 10 and 11)and 43 (FIG. 12). In the embodiment of FIG. 12, the entire radiationshielding chamber 43 communicates with the housing interior 44. In fact,

this radiation-shielding chamber-43d FIG. 12 is formed from the wall ofthe housing itself, taking the form of a groove which is cut into theside wall of'the housing. FIGS. 10 and 11, however, demonstrate that theradiation-shielding chamber can include two or more chamber portionswhich do not communicate with each other. Thus, it will be seen that inFIGS. 10 and 11 the radiation-shielding chamber. portions 5 and 42 donot in fact communicate with each other.

In the special embodiment which is illustrated-in FIG. 14, the outerperipheral edge of the diaphragm 2 extends all the way up to theexterior side surface of the transducer and in fact forms part of theexterior side surface of the transducer. Thus, the exterior side surfaceof the diaphragm 2 of FIG. 14 is situated in a longitudinal extension ofthe exterior side surface of the body 51 which completes the side wallof the housing part 4 and which contributes to the formation of theradiation-shielding gap 5. Thus, in this embodiment theradiation-shielding gap 5 has an outer end which is situated at the sidewall of the transducer and which communicates with the exterior sidesurface of the transducer. In the embodiment of FIG. 13, theradiation-shielding chambers 45 also open onto the exterior surfaces ofthe transducers, but in the illustrated arrangement of a group oftransducers the adjoining chambers 45 communicate with each other sothat one transducer in effect forms the outer limit for theradiation-shielding chamber of an adjoining transducer. However, theentire group of transducers is surrounded by the wall 46, which, ofcourse, limits the outer portions of the radiation-shieldingchambers ofthe outer transducers of the group.

A tongue-and-groove mounting structure 47 is provided for the pluralityof transducers in the embodiment of FIG.

Thus, after the plurality of transducers are assembled so that. theirgrooves, similar to the grooves 26, communicate with each other, theelongated bars or legs 47 of the mounting structure are inserted intothese grooves to form a mounting as illustrated in FIG. 13. Thediaphragms of the individual transducers can be arranged so that eachwill be free to move independently of the remaining diaphragms,although, it is also possible to provide an arrangement where thediaphragms are capable of being interconnected for common movement. Suchan interconnection between a plurality of diaphragms can be providedthrough a structure which may be quite similar to a tongue-and-groovearrangement as shown at 47 in FIG. 13.

The invention, of course, is not limited to the particular embodimentsdescribed above and shown in the drawings. Many variations are possiblewithout departing from the invention, and the transducers canbe used formany different purposes invaddition to those referred to above. Thus,the transducers of the invention can be used in the same way ashereinbefore described at regions of relatively low static pressure, as,for example, in water of low depth. By reason of the particularconstruction hereinbefore described and shown in the drawing, thetransducers of the invention are mechanically particularly robust andstable, so that the largest possible emitting or receiving area for theradiations is provided within a given physical space.

Although in all the embodiments described above the annular shieldingchamber 5 is simply disclosed as being filled with a gas, such as air,it is also possible to provide within the shielding gap 5, a porousmaterial which fills the gap 5 and which has gas-filled cells, forexample, while being relatively soft and elastic so that there is nosubstantial resistance-to displacement of the diaphragm resulting fromthe porous filling material situated in the gap 5 with such aconstruction.

It is apparent that in the aforedescribed structure of the invention,the emitting areas formed by the forwardly directed outer surfaces ofthe diaphragms ofa group of transducers, because they can be effectivelyarranged so close to each other, make it possible to provide an outputof a beam of sharply concentrated primary radiations without detractingessentially therefrom with secondary radiations.

We claim:

1. Electroacoustic transducer for transmitting and receiving sonic wavesin water, suitable for high water pressure and for arrangement intransducer groups, comprising a housing having a front wall forming thefrontal side thereof and a thick side wall having an inside surface insaid housing, a piston-type oscillatory diaphragm structure joined withsaid housing by pressure tight means and forming the front wall thereof,said pressure tight means comprising elastic means in interconnectingsaid diaphragm structure and housing to support said diaphragm structurefor oscillatory movement relative to said housing, an oscillator memberdisposed in said housing be hind said diaphragm structure andmechanically con nected therewith, said diaphragm structure having arear surface in said housing and a front face covering substantially theentire frontal side of said housing and extending to substantially theouter limits of the side wall of said housing, said diaphragm structureand said housing forming a sound-shielding and pressure-tight interspacebehind said diaphragm front face and near and around the perimeter ofsaid diaphragm structure between part of the rear surface of saiddiaphragm structure and part of the inside surface of the side wall ofsaid housing and extending substantially to the front face of saiddiaphragm structure.

2. An electroacoustic transducer as recited in claim 1, wherein saidelastic means defines part of said interference-shielding interspace.

3. A transducer as recited in claim 1, wherein said interspace has anouter substantially annular end opening into the front wall of saidhousing, and further comprising resilient sealing means pressure sealingsaid interspace at its outer end at said front wall of said housing.

4. A transducer as recited in claim 3, and wherein said resilientsealing means is a separate plastic covering material through whichsound can freely pass and which completely envelops the transducer andwhich is situated over and covers said outer end of said interspace.

5. A transducer as recited in claim 3, wherein said resilient sealingmeans forms a connection between said diaphragm and another component ofsaid transducer for supporting said diaphragm for oscillatory movement.

6. A transducer as recited in claim 3-, and wherein said resilientsealing means is of angular cross section and is situated at theexterior of the transducer at the peripheral edge of the front wall ofsaid housing.

7. An electroacoustic transducer for transmitting and receiving sonicwaves in water, suitable for high water pressure and for arrangement intransducer groups, comprising a housing having a front wall forming afrontal side thereof and a thick side wall, said thick side wall havingan outside surface forming the cross sectional area of said housing inthe vicinity of said front wall, a plurality of coactive components insaid housing arranged along a predetermined longitudinal central axis ofthe transducer, said components including a dia phragm joined with saidhousing by pressure-tight means and having an outer forwardly directedsurface adapted to send and receive radiations, said pressure tightmeans comprising elastic means interconnecting said diaphragm andhousing to support said diaphragm for oscillatory movement relative tosaid'housing, said surface of said diaphragm having an area in a planenormal to said axis substantially equal to the cross sectional area ofsaid housing' in the vicinity of said front wall, said diaphragm havinga peripheral edge defining the outer limit of said forwardly directedouter surface thereof and said diaphragm having in the region of saidperipheral edge thereof additional surface area situated to the rear ofsaid forwardly directed diaphragm surface, one of said componentsforming part of the side wall of said housing and being situatedadjacent but spaced from said additional surface area of said diaphragmdecreasing in thickness to a small fraction of the thickness of theremainder of said side wall of said housing as it approaches the frontwall of said housing and extending to form a peripheral edge of saidfront wall of said housing and defining with said additional surfacearea of said diaphragm a pressure-resistant chamber for shielding outinterfering radiations of said additional surface area of saiddiaphragm, said chamber extending substantially to the peripheral edgeof the front wall of said housing formed by said one of said componentsforming part of said side wall of said housing.

8. A transducer as recited in claim 7, wherein said elastic means formsa wall which has a surface defining part of said chamber, said chamberopening into the front wall of said housing, and further comprisingresilient sealing means pressure sealing said chamber at its opening atsaid front wall of said housing.

9. A transducer as recited in claim 8, wherein said wall seperates ahollow interior of said housing from said chamber.

10. An electroacoustic transducer as recited in claim 7, wherein saidelastic means is situated behind said forwardly directed surface of saiddiaphragm, said chamber opening into the front wall of said housing, andfurther comprising resilient sealing means pressure sealing said chamberat its opening at said front wall of said housing.

11. A transducer as recited in claim 10, wherein said diaphragm has aninner rearwardly directed surface, said elastic means being situated inthe region of said inner rearwardly directed surface of said diaphragm.

12. A transducer as recited in claim 7, wherein said chamber has theconfiguration of a narrow annular gap surrounding said axis, saidchamber opening into the front wall of said housing, and furthercomprising resilient sealing means pressure sealing said chamber at itsopening at said front wall of said housing.

13. A transducer as recited in claim 12, wherein said gap extends fromsaid elastic means, on the one hand, outwardly to said forwardlydirected surface of said diaphragm, on the other hand.

14. A transducer as recited in claim 12, wherein said componentcomprises a housing portion separate from and connected tothe remainderof said housing and defining an outer limiting surface of said gap, saidportion of said housing-being separable from and separately connectedthereto in order to facilitate the manufacture of the surfaceswhich-define said gap.

15. A transducer as recited in claim 7, said resilient sealing meansextends along and forms part of a cylinder whose axis coincides withsaid longitudinal central axis.

16. A transducer as recited in claim 7, wherein said housing portionextends forwardly beyond said elastic means and surrounds saiddiaphragm, said forwardly extending portion of said housing having aninner funnel-shaped surface directed toward and spaced from saidadditional surface area of said diaphragm to define therewith saidshielding chamber, said forwardly extending portion of said housingterminating substantially at the same plane as said outer peripheraledge of said forwardly directed surface of said diaphragm.

17. A transducer as recited in claim 16, wherein a carrier is connectedby said elastic means to said housing, said diaphragm being cemented tosaid carrier.

18. A transducer as recited in claim 17, wherein said diaphragm has asurface directed toward said carrier formed with recesses for receivingcement which fixes said diaphragm to said carrier.

19. An electroacoustic transducer assembly comprising a plurality ofelectroacoustic transducers arranged in a group and each comprising ahousing having a front wall forming the frontal side thereof and a thickside wall, said thick side wall having an outside surface forming thecross sectional area of said housing in the vicinity of said front wall,a plurality of components in said housing arranged along a predeterminedlongitudinal central axis and cooperating together to form an operativetransducer, said components of each transducer including a diaphragmjoined with said housing by pressure tight means and having an outerforwardly directed surface adapted to send and receive radiations, saidpressure tight means comprising elastic means interconnecting saiddiaphragm and housing to support,said diaphragm for oscillatory movementrelative to said housing, said diaphragm having an outer peripheral edgedefining the outer limit of said surface, said surface when projectedonto a plane normal to said axis having an area which is at least substantially coextensive with the largest, said group of transducers beingarranged with all of said forwardly directed outer surfaces thereofsituated adjacent each other so that said peripheral edges of saidforwardly directed surfaces are close to each other providing a minimumof space between said diaphragms of the transducers which form said"group of transducers, and each transducer having additional surface areain the region of said peripheral edge of its forwardly directed outersurface, a second one of the components of each transducer forming partof the side wall of said housing and defining with said additionalsurface area thereof a shielding chamber for shielding interferingradiations from said additional surface area of each diaphragmdecreasing in thickness to a small fraction of the thickness of theremainder of said side wall of said housing as it approaches the frontwall of said housing and extending to form a peripheral edge of saidfront wall of said housing, said chamber extending substantial-ly to theperipheral edge of the front wall of said housing formed by said one ofsaid components forming part of said side wall of said housing.

20. A transducer assembly -as recited in claim 19, wherein said.components of each transducer includes a transducer housing formed at'anexterior portion with a depression, and said depressions'of all of saidhousings cooperating to form predetermined passages, and connectingmeans extending into said passages formed by said depressions forinterconnecting said housings of said plurality of transducers to eachother with a minimum of space therebetween so as to maintain the spacebetween.

the housings of the group of transducers at a minimum.

21. A transducer assembly as recited in claim 19, further comprising anenvelope which covers and is common to the group of transducers.

22. A transducer assembly as recited in claim 19, further comprising acurved base plate which carries the entire group of transducers.

23. An electroacoustic transducer, comprising a plurality of coactivecomponents arranged along a predetermined longitudinal central axis ofthe transducer and having an outer side surface, said componentsincluding a diaphragm having an outer forwardly directed surface adaptedto send and receive radiations, and said surface of said diaphragm whenprojected onto a plane normal to said axis having in said plane an areawhich is at least substantially coextensive with the largest areaprojected onto said plane by any other one of said components, saiddiaphragm having a peripheral edge defining the outer limit of saidforwardly directed outer surface thereof and said diaphragm having inthe region of said peripheral edge thereof additional surface areasituated to the rear of said forwardly directed diaphragm surface, andat least a second one of said components being situated adjacent butspaced from the additional surface area of said diaphragm and definingwith said additional surface are-a a pressure-resistant chamber forshielding out interfering radiations of the additional surface area ofsaid diaphragm, said chamber having the configuration of a narrowannular gap surrounding said axis and having an annular outer open endopening onto the outer side surface of said components.

24. An electroacoustic transducer, comprising a plurality of coactivecomponents arranged along a predetermined longitudinal central axis ofthe transducer, said components including a diaphragm having an outerforwardly directed surface adapted to send and receive radiations, andsaid surface of said diaphragm when projected onto a plane normal tosaid axis having in said plane an area which is at least substantiallycoextensive with the largest area projected onto said plane by any otherone of said components, said diaphragm having a peripheral edge definingthe outer limit of said forwardly directed outer surface thereof andsaid diaphragm having in the region of said peripheral edge thereofadditional surf-ace area situated to the rear of said forwardly directeddiaphragm surface, and at least a second one of said components beingsituated adjacent but spaced from the additional surface area of saiddiaphragm and defining with said additional surface area apressure-resistant chamber for shielding out interfering radiations ofthe additional surface area of said diaphragm, said chamber having theconfiguration of a narrow annular gap surrounding said axis and havingouter and inner ends, the outer end of said annular gap being situatednearer to the forwardly directed surface of said diaphragm than theinner end of said gap and said gap having a non-uniform width betweenthe ends thereof but having its minimum width at its outer end andresilient sealing means pressure sealing said gap at its outer end atthe outer forwardly directed surface of said diaphragm.

25. An electroacoustic transducer, comprising a plurality of coactivecomponents arranged along a predetermined longitudinal central axis ofthe transducer, said components including a housing, a diaphragm havingan outer forwardly directed surface adapted to send and receiveradiations, and said surface of said diaphragm when projected onto aplane normal to said axis having in said plane an area which is at leastsubstantially coextensive with the largest area projected onto saidplane by any other one of said components, said diaphragm having aperipheral edge defining the outer limit of said forwardly directedouter surface thereof and said diaphragm having in the region of saidperipheral edge thereof additional surface area situated to the rear ofsaid forwardly directed diaphragm surface elastic means connecting saiddiaphragm to said housing for oscillatory movement relative thereto,said elastic means being adapted to yield in a narrow range situated inthe region of the maximum pressure resistance of which said elasticmeans is capable, protective means for protecting said elastic meansagainst failure in the region of said maxi mum pressure to which saidelastic means can besubjected before failing, and said housing beingsituated adjacent but spaced from the additional surface area of saiddiaphragm and defining with said additional surface area apressure-resistant chamber for shielding out interfering radiations ofthe additional surface area of said diaphragm, said chamber having theconfiguration of a narrow annular gap having a predetermined minimumwidth and the portions of said diaphragm and housing which determinesaid minimum width of said gapforming said protective means and engagingeach other before the flow limit of said elastic means is reached whenthe latter is subjected to pressure.

26. An electroacoustic transducer, comprising a plurality of coactivecomponents arranged along a predetermined -longitudinal central axis ofthe transducer, said components including a housing, a diaphragm havingan outer forwardly directed surface adapted to send and receiveradiations, and said surface of said diaphragm when projected onto aplane normal to said axis having in said plane an area which is at leastsubstantially coextensive with the largest area projected onto saidplane by any other one of said components, said diaphragm having aperipheral edge defining the outer limit of said forwardly directedouter surface thereof and said diaphragm having in the region of saidperipheral edge thereof additional surface area situated to the rear ofsaid forwardly directed diaphragm surface elastic means connecting saiddiaphragm to said housing for oscillatory movement relative thereto,said elastic means being adapted to yield in a narrow range situated inthe region of the maximum pressure resistance of which said elasticmeans is capable, protective means for protecting said elastic meansagainst failure in the region of said maximum pressure to which saidelastic means can be subjected before failing, and said housing beingsituated adjacent but spaced from the additional surface area of saiddiaphragm and defining with said additional surface area apressure-resistant chamber for shielding out interfering radiations ofthe additional surface area of said diaphragm, said housing comprising apair of housing parts separate from but located closely adjacent to eachother, and said protective means being formed by a compressible sealsituated between and engaging said housing parts and stop surfaces resectively forming portions of said housing parts and engaging each otherto limit the extent to which said seal can be compressed as well as tolimit the extent of stressing of said elastic means, said elastic meansbeing operatively connected with one of said housing parts so that saidone housing part will compress said seal when the maximum possiblestressing of said elastic means, before failure thereof, is approached.

27. An electroacoustic transducer assembly comprising a plurality ofelectroacoustic transducers arranged in a group and each comprising ahousing having a front wall forming the frontal side thereof and a thickside wall, a plurality of components in said housing arranged along apredetermined longitudinal central axis and co operating together toform an operative transducer, said components of each transducerincluding a diaphragm joined with said housing by pressure tight meansand having an outer forwardly directed surface adapted to send andreceive radiations, said pressure tight means comprising elastic meansinterconnecting said diaphragm and housing to support said diaphragm foroscillatory movement relative to said housing, said diaphragm having anouter peripheral edge defining the outer limit of said surface, saidsurface when projected onto a plane normal to said axis having an areawhich is at least substantially coextensive wtih the largest areaprojected onto being arranged with all of said forwardly directed outersurfaces thereof situated adjacent each other so that said peripheraledges of said forwardly directed surfaces are close to each otherproviding a minimum of space between said diaphragms of the transducerswhich form said group of transducers, and each transducer havingadditional surface area in the region of said peripheral edge of itsforwardly directed outer surface, a second one of the components of eachtransducer forming part of the side wall of said housing and definingwith said additional surface area thereof a shielding chamber forshielding transferring radiations from said additional surface area ofeach diaphragm, said chamber extending substantially to the outersurface of said'diaphragm, each transducer limiting the shieldingchamber of its adjoining transducers, and limiting means surrounding theentire group of transducers for limiting the sound-shielding chambers ofthe transducers situated along the exterior of the group of transducers.

28. An electroacoustic transducer assembly comprising a plurality ofelectroacoustic transducers arranged in a group and each comprising ahousing having a front wall forming the frontal side thereof and a thickside wall, a plurality of components in said housing arranged along apredetermined longitudinal central axis and cooperating together to forman operative transducer, said components of each transducer including adiaphragm joined with said housing by pressure tight means and having anouter forwardly directed surface adapted to send and receive radiations,said pressure tight means comprising elastic means interconnecting saiddiaphragm and housing to support said diaphragm for oscillatory movementrelative to said housing, said diaphragm having an outer peripherealedge defining the outer limit of said surface, said surface whenprojected onto a plane normal to said axis having an area which is atleast substantially co extensive with the largest area projected ontosaid plane by said housing, said group of transducers being arrangedwith all of said forwardly directed outer surfaces thereof situatedadjacent each other so that said peripheral edges of said forwardlydirected surfaces are close to each other providing a minimum of spacebetween said diaphragms of the transducers which form said group oftransducers, and each transducer having additional surface area in theregion of said peripheral edge of its forwardly directed outer surface,a second one of the components of each transducer forming part of theside wall of said housing and defining with said additional surface areathereof a shielding chamber for shielding transferring radiations fromsaid additional surface area of each diaphragm, said chamber extendingsubstantially to the outer surface of said diaphragm, the shieldingchambers of adjoining transducers communicating with each other to formcommon shielding chambers defined in part by the additional surfaceare-as of said diaphragms.

References Cited by the Examiner UNITED STATES PATENTS RODNEY D.BENNETT, Plimary Examiner.

CHESTER L. JUSTUS, Examiner. G. M. FISHER, B. L. RIBANDO, AssistantExaminers.

1. ELECTROACOUSTIC TRANSDUCER FOR TRANSMITTING AND RECEIVING SONIC WAVESIN WATER, SUITABLE FOR HIGH WATER PRESSURE AND FOR ARRANGEMENT INTRANSDUCER GROUPS, COMPRISING A HOUSING HAVING A FRONT WALL FORMING THEFRONTAL SIDE THEREOF AND A THICK SIDE WALL HAVING AN INSIDE SURFACE INSAID HOUSING, A PISTON-TYPE OSCILLATORY DIAPHRAGM STRUCTURE JOINED WITHSAID HOUSING BY PRESSURE TIGHT MEANS AND FORMING THE FRONT WALL THEREOF,SAID PRESSURE TIGHT MEANS COMPRISING ELASTIC MEANS IN INTERCONNECTINGSAID DIAPHRAGM STRUCTURE AND HOUSING TO SUPPORT SAID DIAPHRAGM STRUCTUREFOR OSCILLATORY MOVEMENT RELATIVE TO SAID HOUSING, AN OSCILLATOR MEMBERDISPOSED IN SAID HOUSING BEHIND SAID DIAPHRAGM STRUCTURE ANDMECHANICALLY CONNECTED THEREWITH, SAID DIAPHRAGM STRUCTURE HAVING A REARSURFACE IN SAID HOUSING AND A FRONT FACE COVERING SUBSTANTIALLY THEENTIRE FRONTAL SIDE OF SAID HOUSING AND EXTENDING TO SUBSTANTIALLY THEOUTER LIMITS OF THE SIDE WALL OF SAID HOUSING, SAID DIAPHRAGM STRUCTUREAND SAID HOUSING FORMING A SOUND-SHIELDING AND PRESSURE-TIGHT INTERSPACEBEHIND SAID DIAPHRAGM FRONT FACE AND NEAR AND AROUND THE PERIMETER OFSAID DIAPHRAGM STRUCTURE BETWEEN PART OF THE REAR SURFACE OF SAIDDIAPHRAGM STRUCTURE AND PART OF THE INSIDE SURFACE OF THE SIDE WALL OFSAID HOUSING AND EXTENDING SUBSTANTIALLY TO THE FRONT FACE OF SAIDDIAPHRAGM STRUCTURE.